1. Field of the Invention
This invention relates generally to the field of bicycle suspensions. More particularly, the invention relates to a damping enhancement system for a bicycle.
2. Description of the Related Art
For many years bicycles were constructed using exclusively rigid frame designs. These conventional bicycles relied on air-pressurized tires and a small amount of natural flexibility in the frame and front forks to absorb the bumps of the road and trail. This level of shock absorption was generally considered acceptable for bicycles which were ridden primarily on flat, well maintained roads. However, as xe2x80x9coff-roadxe2x80x9d biking became more popular with the advent of All Terrain Bicycles (xe2x80x9cATBsxe2x80x9d), improved shock absorption systems were needed to improve the smoothness of the ride over harsh terrain. As a result, new shock absorbing bicycle suspensions were developed.
Two such suspension systems are illustrated in FIGS. 1 and 2. These two rear suspension designs are described in detail in Leitner, U.S. Pat. No. 5,678,837, and Leitner, U.S. Pat. No. 5,509,679, which are assigned to the assignee of the present application. Briefly, FIG. 1 illustrates a telescoping shock absorber 110 rigidly attached to the upper arm members 103 of the bicycle on one end and pivotally attached to the bicycle seat tube 120 at the other end (point 106). FIG. 2 employs another embodiment wherein a lever 205 is pivotally attached to the upper arm members 203 and the shock absorber 210 is pivotally attached to the lever 205 at an intermediate position 204 between the ends of the lever 205.
There are several problems associated with the conventional shock absorbers employed in the foregoing rear suspension systems. One problem is that conventional shock absorbers are configured with a fixed damping rate. As such, the shock absorber can either be set xe2x80x9csoftxe2x80x9d for better wheel compliance to the terrain or xe2x80x9cstiffxe2x80x9d to minimize movement during aggressive pedaling of the rider. However, there is no mechanism in the prior art which provides for automatic adjustment of the shock absorber setting based on different terrain and/or pedaling conditions.
A second, related problem with the prior art is that conventional shock absorbers are only capable of reacting to the relative movement between the bicycle chassis and the wheel. In other words, the shock absorber itself has no way of differentiating between forces caused by the upward movement of the wheel (i.e., due to contact with the terrain) and forces caused by the downward movement of the chassis (i.e., due to movement of the rider""s mass).
Thus, most shock absorbers are configured somewhere in between the xe2x80x9csoftxe2x80x9d and xe2x80x9cstiffxe2x80x9d settings (i.e., at an intermediate setting). Using a static, intermediate setting in this manner means that the xe2x80x9cidealxe2x80x9d damper settingxe2x80x94i.e., the perfect level of stiffness for a given set of conditionsxe2x80x94will never be fully realized. For example, a rider, when pedaling hard for maximum power and efficiency, prefers a rigid suspension whereby human energy output is vectored directly to the rotation of the rear wheel. By contrast, a rider prefers a softer suspension when riding over harsh terrain. A softer suspension setting improves the compliance of the wheel to the terrain which, in turn, improves the control by the rider.
Accordingly, what is needed is a damping system which will dynamically adjust to changes in terrain and/or pedaling conditions. What is also needed is a damping system which will provide to a xe2x80x9cstiffxe2x80x9d damping rate to control rider-induced suspension movement and a xe2x80x9csoftxe2x80x9d damping rate to absorb forces from the terrain. Finally, what is needed is a damping system which will differentiate between upward forces produced by the contact of the wheel with the terrain and downward forces produced by the movement of the rider""s mass.
A bicycle shock absorber for differentiating between rider-induced forces and terrain-induced forces comprising: a first fluid chamber having fluid contained therein; a piston for compressing the fluid within the fluid chamber; a second fluid chamber coupled to the first fluid chamber by a fluid communication hose; and an inertial valve disposed within the second fluid chamber, the inertial valve opening in response to terrain-induced forces and providing communication of fluid compressed by the piston from the first fluid chamber to the second fluid chamber; and the inertial valve not opening in response to rider-induced forces and preventing communication of the fluid compressed by the piston from the first fluid chamber to the second fluid chamber.